Process and guidance system for ensuring reliable guidance of a vehicle

ABSTRACT

A process for guiding a vehicle along a route to a predetermined destination point includes determining a route in the form of consecutive path points which include at least geographic coordinates, determining the linear distance between a current location and the next path point and/or determining a change in the direction of travel between path points or at a path point. The process also provides a departure from route warning if (1) the linear distance is the next path point is more than a predetermined value; (2) a change in direction between path points lies outside of an allowed range or (3) a change in direction at a path point deviates from a target change in direction by more than a predetermined tolerance value.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a process and a guidance system for ensuringreliable guidance of a vehicle along a route to a predetermineddestination point, in which the current location of the vehicle isascertained and a route is determined in the form of consecutive pathpoints comprising at least the geographic coordinates. The route isdisplayed to the vehicle driver in the form of driving instructions. Anydeparture from the preestablished route is signalled as soon as apreestablished decision criterion is met.

2. Description of the Prior Art

Vehicle guidance systems with visible and/or audible output devices fordriving instructions to guide a vehicle along an advantageous determinedroute to a preestablished destination point are known. For driversunfamiliar with an area, for example, these systems display the currentlocation and the route, as well as all impending changes in direction,in the form of driving instructions based on digitalized road mapsstored in the vehicle or externally.

DE 4039887 A1 discloses a process wherein the current location isascertained by a locating system installed in the vehicle. A routeleading from the current location to a preestablished destination pointis determined by at least one external computer of an off-boardnavigational system. This route is transmitted to the vehicle in theform of a sequence of road segments to be traversed (a so-called guidevector chain), together with a road map of the immediate surroundings,and is displayed on a display device. The external computers areinstalled in spatially distributed beacons and can also be connected toa traffic computer. The guide vector chain comprises the geographiccoordinates of the road segments to be traversed, and thus makes itpossible to compare these geographic coordinates with the currentlocation of the vehicle. Based on the results of this comparison, it ispossible to display the current location of the vehicle, together withdriving instructions, to the driver on the display device, and thus tosuccessively guide the driver to the preestablished destination. Thus,in this process, guidance is always provided starting from the currentlocation of the vehicle, regardless of whether or not the vehicle hasdeviated from the preestablished route of travel.

Although this process is suitable for guiding vehicles with the help ofan off-board navigation system, in particular, it does not detectdeviations from the preestablished route and thus does not communicatesuch deviations to the driver. In this process, only when a beacon ispassed does the computer select, based on the current location of thevehicle (or the beacon), at least one guide vector chain leading to thepreestablished destination from a guide vector chain collective. Theselected guide vector chain is then transmitted to the vehicle anddisplayed to the driver directly or in the form of driving instructions.This is how “error correction” is undertaken in the event of deviationsfrom the original route.

DE 36 45 100 C2 discloses a navigation system for motor vehicles inwhich a map memory device must be carried in the vehicle and the routeis established as a sequence of so-called “highlighted” points. Thissystem has sensors in the vehicle that ascertain the direction of travelas well as the path that has been travelled by the vehicle. The systemis therefore able to reproduce the geometric shape of the traversedpath, so that, starting from an initial point, the current location ofthe vehicle is ascertained. Due to the limited accuracy of the datacollection, there is inevitably an ongoing summation of error variables.To prevent these errors from assuming uncontrollable orders of magnitudein the current location, this navigation system, when a new“highlighted” path point is reached, replaces the data of the computedlocation with the actual location data of the path point reached. Thefact that a new path point has indeed been reached is recognized becausethe length of the path between each two consecutive “highlighted” pathpoints (i.e., the road distance) is recorded in the map memory device asa target value. The path actually travelled by the vehicle between twosuch path points is continually subtracted from this target value. Whenthe difference obtained in this manner approaches zero, the “added up”location is supposed to correspond to the location of the aimed-at pathpoint preestablished by the map memory device. If, instead, animpermissibly large difference results, the system issues a warning thatthe predetermined route has been deviated from. Such a warning is alsoissued as soon as the “added up” location of the vehicle, during a tripbetween the two adjacent “highlighted” path points, leaves a definederror zone around these path points. The shape of this error zone issubstantially rectangular. Its width (at a right angle to the road) ishalf as large as the linear distance between the two path points. In theevent of unplanned detours, this system, due to the relatively broaderror zone between the consecutive path points, may not recognize untilvery late (for example, not until the next path point should have beenreached) deviations that have occurred from the preestablished route.

SUMMARY OF THE INVENTION

The object of the present invention is to indicate a process for thereliable guidance of a vehicle along an advantageous route determined,in particular, with the help of an off-board navigation system, and aguidance system to implement this process, in which, with the leastpossible technical expense, deviations from the preestablished route arerecognized as quickly as possible in the vehicle, without a digital roadmap or the like having to be carried in the vehicle for this purpose.

According to a first aspect of the present invention, this object isattained in that a route is initially determined in the form ofconsecutive path points. The current location of the vehicle iscontinually ascertained by the guidance system in the vehicle based ondata or signals that are transmitted wirelessly to the vehicle guidancesystem. Based on the current determined location, the linear distance tothe next path point that the vehicle is to pass on its route iscontinually compared with a predetermined minimum value. Thepredetermined minimum value initially corresponds to the linear distance(straight line) of the particular sequential path points. The lineardistance can differ significantly (especially on curving roads) from theactual length of the route between these path points. The predeterminedminimum value is replaced by a calculated linear distance when thelinear distance is smaller than the previous predetermined minimumvalue. Departure from the preestablished route is signalled to thedriver when the calculated linear distance exceeds the current minimumvalue by a predetermined threshold value. As soon as the next path pointis reached, the linear distance to the next path point is set the sameway as the initial predetermined minimum value.

The process according to the invention makes it possible, with littletechnical expense, to immediately detect deviations from apreestablished route and to display these to the driver without adigital road map of suitable resolution having to be carried in thevehicle. The guidance system in the vehicle can be very simplyconstructed, especially when the route is determined with the help of anoff-board navigation system and transmitted to the vehicle in the formof path points. In such cases, the guidance system needs only an inputand output unit, a location sensor system and a data communicationsdevice. Advantageously, the path points of the route comprise at leastthe geographic coordinates, so that a direct comparison with thelocation data of the vehicle is possible.

If guidance is carried out by an off-board navigation system thatdetermines a suitable route and transmits it to the vehicle in the formof path points, especially reliable guidance is attained by means of thesimple process according to the invention, because any incorrect turnwill be immediately recognized in the vehicle, so that, very soon aftera wrong route is taken, it can be identified as such and then corrected.Especially high reliability in recognizing wrong routes can be attainedwhen the process according to the inventions combined with a process forrecognizing an incorrect route based on other principles. For example,one process or the other can be used for certain predetermined segments,depending on which process is best suited for the characteristics of thesegment in question.

According to a first embodiment of the invention, a guidance system forthe reliable guidance of a vehicle that immediately recognizes anydeviation from a preestablished route comprises an input device,particularly for entering a destination point, and a locationdetermination device for determining the current geographic location ofthe vehicle. To ascertain the vehicle location, a remote locationdetermination device processes data or signals transmitted wirelessly tothe vehicle. A route connecting the current location and the destinationpoint is determined in the vehicle by the guidance system or outside thevehicle, and is then stored in a memory of the guidance system in theform of path points. A distance determination/comparison device permitsthe linear distance between the current vehicle location and the nextpath point that the vehicle will pass on its route to be ascertainedcontinually and compared with a preestablished minimum value. When thecalculated distance exceeds the minimum value by a preset thresholdvalue, a warning signal can be triggered by the distancedetermination/comparison device to alert the driver of the vehicle thathe has deviated from the preestablished route. Measures to correct theroute may also be initiated by a suitable signal. In contrast, after acomparison, the preset minimum value is replaced by the determinedlinear distance when the determined distance is smaller than the minimumvalue, i.e., under these conditions, the most recently ascertainedlinear distance becomes the new minimum value.

To account for the specific form of the route leading to thedestination, it is possible to set an individual threshold value forindividual sections of the route. This is advantageously done by adevice with the digital road map for determining the route, i.e., in thecase of an off-board system, a vehicle-external traffic computer.

Preferably, an on-board computer, which is preferably embodied as acalculating program, controls the distance determination/comparisondevice. It is especially suitable, in the guidance system with anoff-board navigation system, for the latter to also be equipped with acommunications device for data exchange. The communications device canserve to transmit the route in the form of path points from theoff-board navigation system to the guidance system. Advantageously, thecommunications device is embodied as a mobile telephone. The embodimentof the input device as a keyboard has proved to be a universal solution.When embodied as a receiver for satellite navigation signals, thelocation determination device is small and easy to house. The inventionproposes that, upon any deviation from the preestablished route, apreferably visual warning signal be displayable on the display device,in particular, together with driving instructions, by means of theon-board computer. The driving instructions can contain detailedinformation on the deviation from the preestablished route. Of course,the warning signal could also be issued in a different form such, forexample, as an audible signal.

According to a second embodiment of the invention, the route isinitially determined in the form of consecutive path points comprisingat least the geographic coordinates. For example, the current directionof travel and the current location of the vehicle are continually foundbetween the path points by means of locating or directional sensors. Thecurrent direction of travel is compared with the previous direction oftravel, ascertained a short time before, to determine the change indirection. It is especially advantageous to use data or signalstransmitted wirelessly to the vehicle to determine the current locationand/or direction of travel (e.g., signals of a satellite navigationsystem). A deviation from the preestablished route exists when the sizeof the ascertained change in the direction of travel lies outside of apreset value range. In such cases, the driver is notified by signal thathe has departed from the preestablished route, or else measures tocorrect the route are initiated.

The permissible value ranges for changes in direction can be establishedfor all segments of the road network at the same time. In some cases,however, it is advantageous to establish these values individually forindividual sections. The path points determining the route can be atdifferent distances from each other. Their advantageous distance isbased on the geometric course of the road (curves, possible turns,etc.).

The process according to the second embodiment of the invention allowsdeviations from a preestablished route of travel to be immediatelyrecognized and displayed to the driver with little technical expense andwithout a digital road map of suitable resolution having to be carriedin the vehicle. The guidance system in the vehicle can be constructedespecially simply when the route is determined outside the vehicle andtransmitted to the vehicle in the form of path points. In such cases,the guidance system needs only an input and output unit, a locationsensor system, and a data communications device. Because the path pointsof the route comprise at least the geographic coordinates, a directcomparison with the geographic location data of the vehicle is possible.

Advantageously, the change in direction is ascertained from direction oftravel values determined as the average values of the direction oftravel for short predetermined sections. It is thereby advantageous,particularly for the purpose of increasing, in a simple manner, thereliability of the information gained from the process, to determine thecurrent direction of travel as the average direction of travel in apredetermined first section, one of whose end points forms the currentgeographic location, and to determine the previous direction of travelas the average direction of travel in a preestablished second section,whereby the first section advantageously immediately follows the secondsection. It is especially advantageous for the first and second sectionsto have the same length. As an alternative, it is also possible for thetwo sections to partially overlap each other.

When guidance is carried out by an off-board navigation system thatdetermines a favorable route of travel and transmits it to the vehicle,the very simple process according to the invention nonetheless ensuresreliable guidance, whereby a wrong route can be recognized and correctedvery quickly after being embarked upon. Especially high reliability inrecognizing wrong routes can be attained when the process according tothe invention is combined with a process for recognizing wrong routesbased on different principles, so that one process or the other is used,for example, for certain predetermined sections, depending on whichprocess is best suited for the characteristics of the section inquestion.

A guidance system according to the second embodiment of the inventionfor the reliable guidance of a vehicle, which system immediatelyrecognizes any departure from a preestablished route, comprises an inputdevice for entering a destination point and a location determinationdevice for determining the current location. A route connecting thecurrent location and the destination point is determined in the vehicleby the guidance system or outside of the vehicle and is stored in amemory device of the guidance system in the form of path points. Achange in direction determination device allows the current direction oftravel of the vehicle to be continually determined between the pathpoints and then compared with the direction of travel ascertained ashort time before. Specifically, the change in direction determinationdevice can issue a control signal when the size of the ascertainedchange in direction lies outside a preestablished value range that cancontain, in particular, a preestablished maximum value. Thus, anydeparture from the preestablished route can be displayed to the driver,having been triggered, for example, by a warning signal.

Preferably, there is an on-board computer controlling the change indirection determination device, which preferably is embodied as acalculating program. In a guidance system with an off-board navigationsystem, it is especially suitable for the off-board navigation system toalso be equipped with a communications device for data exchange. Thecommunications device allows the travel route to be transmitted to theguidance system by the off-board navigation system in the form of pathpoints. Advantageously, the communications device is embodied as amobile phone. The embodiment of the input device as a keyboard hasproved to be a universal solution. The location determination device issmall and easy to house when it has a receiver for satellite navigationsignals. These satellite signals are also suitable for determining thecurrent direction of travel. Alternatively, the direction of travel canbe found, for example, with the help of a magnetic field probe. Theinvention proposes that upon departure from the route of travel, anoptical warning signal be displayable on the display device, inparticular, together with driving instructions, by means of the on-boardcomputer. The driving instructions can contain detailed information onthe deviations from the preestablished route.

According to a third embodiment of the invention, the route is againinitially determined in the form of consecutive path points, whichcomprise at least the geographic coordinates. Those path points that arealso turn points, i.e., path points that are located withinintersections or junctions where a change in direction is planned, areeach assigned a target turn angle. Further, the current location and thecurrent direction of travel of the vehicle are continually ascertained.It is especially advantageous to use data or signals transmittedwirelessly to the vehicle to find the current geographic location and/ordirection of travel (e.g., signals of a satellite navigation system).When the vehicle passes a path point having a target turn angle, theturn angle of the vehicle is ascertained. This ascertained turn angle isthen compared with the target turn angle. If the found turn angledeviates by more than a predetermined tolerance value from the targetturn angle, the driver is notified by signal of a departure from thepreestablished route, or else measures to correct the route areinitiated. The tolerance value can be preestablished in a blanketfashion or can be stored individually for all or some path pointstogether with the turn angle.

The process according to the third embodiment of the invention allowsany deviations from a preestablished route to be recognized and reportedto the driver immediately with low technical expense and without adigital road map of suitable resolution having to be carried in thevehicle for this purpose. The guidance system in the vehicle can beconstructed in an especially simple manner when the route is determinedoutside of the vehicle and transmitted to the vehicle in the form ofpath points. The guidance system in such cases needs only an input andoutput unit, a locating sensor system and a data communications device.Because the path points of the route comprise at least the geographiccoordinates, a direct comparison with the geographical location data ofthe vehicle is possible. The actual location of the vehicle ispreferably ascertained on the basis of data or signals transmittedwirelessly to the vehicle, i.e., by radio direction finding, especiallypreferably by satellite navigation.

In one embodiment of the third embodiment of the invention, the turnangle and the target turn angle are relative angles in relation to thechange in direction of the vehicle at the given intersection orjunction. In a further embodiment, the turn angle and the target turnangle are absolute angles in relation to the direction of travel(directional point) after the particular intersection or junction.However, it is also possible to advantageously combine the twoembodiments of the invention in such a way that some intersections orjunctions are assigned the target change in direction as the target turnangle, while other intersections or junctions are assigned the targetdirection of travel as the target turn angle.

Advantageously, the direction of travel is ascertained as an averagevalue in that the direction of travel at each of several directlyconsecutive geographic locations is determined. To reduce randomdistributions of the direction of travel values and obtain only the maindirection of travel of the vehicle, the arithmetic average value iscalculated from these directions of travel (e.g., continually, as asliding average value). Preferably, the change in direction at one pathpoint is found by calculating the difference from the main direction oftravel (i.e., the average direction of travel) directly before anddirectly after the path point.

When guidance is carried out by an off-board navigation system thatdetermines a favorable route and transmits it to the vehicle in the formof path points, reliable guidance is attained by the process despite thelow technical expense. Wrong routes are recognized a very short timeafter being embarked upon, and can then be corrected. Especially highreliability in recognizing a wrong route can be attained when thepresent process is combined with a process for recognizing wrong routebased on other principles, so that, for example, one process or theother is used for certain predetermined sections, depending on whichprocess is best suited for the characteristics of the section inquestion. In particular, the combined use of the process according tothe three embodiments of the present invention is advantageous.

A guidance system according to the third embodiment of the invention forthe reliable guidance of a vehicle, which system can immediatelyrecognize any departure from a preestablished route again comprises aninput device, in particular, for entering a destination point, and alocation determination device for determining the current location ofthe vehicle. A route connecting the current location and the destinationpoint, which can be determined in the vehicle by means of the guidancesystem or outside of the vehicle, is stored in a working memory of theguidance system. The route is stored in the form of consecutive pathpoints, which comprise at least the geographic coordinates. At least forthose intersections or junctions where a change in direction is planned,a target turn angle is assigned to the associated path point lyingwithin the intersection or junction, and this target turn angle is alsostored in the working memory. A direction of travel determination deviceand a change in direction determination device are also provided andserve, when the vehicle passes a path point to which a target turn angleis assigned, to ascertain the actual turn angle of the vehicle. Acomparison device is provided to compare the ascertained turn angle withthe target turn angle. A warning signal that signals a departure fromthe preestablished route to the driver, for example, can be triggeredwhen the direction of travel deviates from the target direction oftravel or when the change in direction deviates from the target changein direction by more than a predetermined tolerance value.

Preferably, an on-board computer controls the direction of traveldetermination device and the change in direction determination device,which are preferably embodied as a calculating program. It is especiallysuitable, in the guidance system with an off-board navigation system,for the latter to also be equipped with a communications device for dataexchange. The communications device allows the route to be transmittedby the off-board navigation system to the guidance system in the form ofpath points. Advantageously, the communications device is embodied as amobile telephone. The embodiment of the input device as a keyboard hasproved to be a universal solution. The geographic location determinationdevice is small and easy to house when it has a receiver for satellitenavigation signals. These satellite signals are also suitable forascertaining the current direction of travel. Alternatively, thedirection of travel can be determined, for example, with the help of amagnetic field probe. The invention proposes that, upon any departurefrom the route, a preferably visual warning signal be displayable on thedisplay device, in particular, together with driving instructions, bymeans of the on-board computer. The driving instructions can containdetailed information on the deviations from the preestablished route. Ofcourse, the warning signal can also be emitted in other ways such, forexample, as with an audible signal.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, wherein like reference characters denote similarelements:

FIG. 1 is a block diagram of an embodiment of a vehicle navigationsystem according to the present invention;

FIG. 2 is a block diagram of another embodiment of the vehiclenavigation system according to the present invention; and

FIG. 3 is a block diagram of yet another embodiment of the vehiclenavigation system according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A vehicle navigation system shown in FIG. 1 comprises a guidance system10 installed in the vehicle. The guidance system 10 has an on-boardcomputer 11, by means of which the other components 12 to 19 of theguidance system 10 are connected to one another and can be controlled.An input device 12 in the form, for example, of a keyboard permits theinput of the destination point, for example, a street name. Thespecified destination point can be stored in the memory 13 and is thusavailable to be called up as needed. To determine the current vehiclelocation, the guidance system 10 has a receiver 14 of a satellitenavigation system (e.g., GPS=Global Positioning System), which receiver14 is also connected in terms of data transmission to the on-boardcomputer 11. As needed, the current location which is continuallydeterminable from the received satellite signals can be stored by theon-board computer 11 in the memory 13. In addition, the most favorabledetermined route, based on the current location and the inputdestination point, is stored in the memory 13 in the form of path pointsthat contain the geographic data. As FIG. 1 shows, the guidance system10 has a display device 15 equipped with an visual display, such, forexample, as a video screen by means of which the route can be displayed,together with the driving instructions, under the partial or completecontrol of the on-board computer 11. The current vehicle location isthereby displayed highlighted by color, for example. A distancedetermination/comparison device 19 determines the linear distance fromthe current vehicle location to the next path point of the two pathpoints between which the vehicle is located at a given moment. Thedistance determination/comparison device 19 compares the determinedlinear distance with a preset minimum value. A warning signal can betriggered, specifically, when the determined linear distance exceeds thepreset minimum value by a preset threshold value. To account, forexample, for the form of the best route leading to the destinationpoint, an individual threshold value is provided for each individualsection of the route. Thanks to the warning signal, a suitable audiblesignal for the driver can be produced by the on-board computer 11 and/orsuitable driving instructions can be issued via the visual display ofthe display device 15. The preset minimum value can be replaced by thecurrent determined linear distance when the previous minimum value isgreater than this determined linear distance. To minimize theequipment-related costs of the guidance system 10, the latter isconnected to a communications device 17, particularly a mobile phone, bymeans of which a data connection can be established to an off-boardnavigation system 20 arranged outside the vehicle. As FIG. 1 shows, theoff-board navigation system 20 is equipped with a transmitter/receiver21 for data exchange with the guidance system 10. The navigation system20 contains a traffic computer 22, which has access to a digital roadmap 23 as well as to current traffic information.

To implement guidance of the vehicle, the driver enters a destinationpoint via the keyboard of the input device 12. The destination point istransmitted, together with the current location of the vehicle asdetermined by means of the receiver 14, to the traffic computer 22 ofthe off-board navigation system 20 by means of the communications device17. Based on the digital road map 23, the traffic computer 22 thendetermines a favorable route to the given destination point. This routeis transmitted back to the guidance system 10 in the form of path pointsand stored in the memory 13 under the control of the on-board computer11. The current vehicle location is determined on the basis of thesignals received by the receiver 14, so that the distancedetermination/comparison device 19 can ascertain the two directlyconsecutive path points between which the vehicle is located at thegiven moment. Further, the distance determination/comparison device 19continually has available the current location of the vehicle as foundby means of the receiver 14. From this, the distancedetermination/comparison device 19 continually calculates the lineardistance (straight line) from the current location to the next pathpoint that the vehicle will pass on its route, and compares thisdistance to a preset minimum value. If the calculated distance isgreater than the minimum value, the preset minimum value is replaced bythe calculated distance. Moreover, if the calculated linear distance forthis section of the route exceeds the previous minimum value by a presetthreshold value, the distance determination/comparison device 19triggers a warning signal to signal a departure from the preset route.Of course, it is also possible, when a warning signal is triggered, todetermine a new route to the destination point and guide the vehiclealong this route without explicitly informing the driver that a wrongroute was taken. The threshold value can also be used to adjust theprocess to the sometimes very complicated course of a given route. Thisis advantageous, for example, when the distance to the next path point,i.e., the straight-line connection between the current location of thevehicle and the next path point, temporarily increases, due to a curvedor looping section, even though the segment still to be travelled tothis path point continues to grow shorter. The warning signal alerts theon-board computer 11 to emit a suitable signal to the driver. The signalcan be emitted acoustically, in the form of a warning tone or a voicemessage, as well as optically on the display device 15. The driver canobtain, especially by means of the visual display, for example,additional information on the deviation from the preset route as well asdriving instructions from the guidance system 10. In an alternativeembodiment of the invention, the distance determination/comparisondevice 19 is embodied as a calculating program, which can be called upby the on-board computer 11.

The embodiment of the present invention shown in FIG. 2 largely agreeswith that in FIG. 1 with respect to the basic functions, so thatreference can be made to FIG. 1 and only differences therefrom arediscussed below.

In this embodiment of the invention, a change in direction determinationdevice 18 is provided instead of the distance determination/comparisondevice 19 shown in FIG. 1. During the trip, the change in directiondetermination device 18 continually receives the current location of thevehicle as determined by the receiver 14. From this, the change indirection determination device 18, to ascertain a change in directionbetween path points, continually calculates the current direction oftravel, compares the calculated current direction of travel with apreviously ascertained direction of travel, and finds the change indirection in the form of the difference between the directions.Preferably, the change in direction is determined from direction valuesthat are found as the average value of directions for preestablishedshort sections of the route. Advantageously, the sections for whichdirection data is found should have the same length. Averaging is donein such a way that the directions of travel at locations directlyfollowing one another in a preestablished section of 50 m, for example,are found, and the average value is calculated from these founddirections of travel. Alternatively or in addition to this, of course,the direction of travel can be determined by the receiver 14 of thesatellite navigation system using an internal calculation process. Thedifference between the current direction of travel and the previousdirection of travel is preferably found in that the current direction oftravel is determined as the average direction of travel in apreestablished first section, one of whose end points is the currentvehicle location, while the previous direction of travel is determinedas the average direction of travel in a preestablished second section,whereby the first section directly follows the second section. Incertain cases, it can be advantageous for the two sections to overlap orbe separated from each other by a distance. The direction of travel andthe change in direction can also be determined in an ongoing (sliding)manner. When the size of the change in direction exceeds a presetmaximum value, a departure from the preestablished route is signalled bya suitable warning, as already described in reference to FIG. 1.

The embodiment of the present invention shown in FIG. 3 agrees largelywith that shown in FIG. 1, so that again the earlier description isreferred to and, for the most part, only the differences therefrom arediscussed below.

The path point data stored in the memory 13 to define the route comprisenot only the geographic coordinates of the locations to be passed, butalso, at least for path points in the area of intersections or junctionswhere a change in direction is to occur, a target turn angle. The targetturn angle is either a relative angle which is the change in directionof the vehicle at the given intersection or junction, or an absoluteangle which is the direction of travel of the vehicle directly after theparticular intersection or junction. As FIG. 3 shows, a change indirection determination device 16 as well as a direction of traveldetermination device 16 a and a comparison device 16 b are providedinstead of the distance determination/comparison device 19 shown in FIG.1. The direction of travel is determined by the direction of traveldetermination device 16 for path points to which an absolute angle isassigned as the target turn angle. Alternatively or in addition thereto,of course, the direction of travel can be determined by the receiver 14of the satellite navigation system using internal calculation processes.The determination of the change in direction for path points to which arelative angle is assigned is carried out by the change in directiondetermination device 16 a. The direction of travel determination device16 and the change in direction determination device 16 a are thereby theessential components of the turn angle determination device. To comparethe direction of travel with the target direction of travelcorresponding to the target turn angle, or to compare the change indirection with the target change in direction corresponding to thetarget turn angle, a comparison device 16 b is provided, and therespective target values can be called up from the memory 13. As inFIGS. 1 and 2, a warning signal to signal a departure from thepreestablished route can be triggered by the comparison device 16 b whenthe direction of travel deviates from the target direction of travel orwhen the change in direction deviates from the target change indirection by more than a preset tolerance value.

To initiate guidance of the vehicle, the destination point is enteredvia the keyboard of the input device 12. The destination point, togetherwith the current location of the vehicle as determined by means of thereceiver 14, is transmitted by the communications device 17 to thetraffic computer 22 of the off-board navigation system 20. Based on thedigital road map 23, the traffic computer 22 then determines a favorableroute to the preestablished destination point. This route is transmittedback to the guidance system 10 in the form of path points. Path pointsthat lie in the area of intersections or junctions where a change indirection is planned, i.e., path points that are also turn points of theroute, are assigned, as a target turn angle, either a target change indirection (relative angle) or a target direction of travel (absoluteangle). The path points, along with the target turn angle (target changein direction, target direction of travel), are stored in the memory 13under the control of the on-board computer 11. The receiver 14continuously determines the current location and the current directionof travel of the vehicle; it is also possible to provide additionaldirection sensors for determining direction of travel. The averagedirection of travel of the vehicle is thus determined in that thecurrent directions of travel are found at a predeterminable number oflocations (e.g., 50) that follow one another directly in the directionof travel, and the average value is calculated from these directions.Instead of a predetermined number of locations, a short section can bepredetermined, and the average value of the respective directions oftravel at each vehicle location in this section can be found. In thisway, the direction of travel determination device 16 ascertains theaverage direction following the path points to which an absolute targetturn angle is assigned. When the vehicle passes a path point to which arelative target turn angle or a target change of direction is assigned,the change in direction determination device 16 a ascertains the changein direction by finding the difference between the average directions oftravel of the vehicle before and after the path point in question. Theascertained direction of travel or change in direction is compared withthe corresponding target value in the comparison device 16 b. If theascertained direction of travel deviates from the target direction oftravel or if the change in direction deviates from the target change indirection by more than a preset tolerance value, a departure from thepreset route is signalled, in that a warning signal to this effect istriggered by the comparison device 16 b.

Alternatively, it is also advantageously possible to assign both arelative and an absolute angle to individual path points or to all pathpoints where a change in direction is planned, and to ascertain both thedirection of travel and the change in direction for these path points.In such an embodiment of the invention, after the comparison with thetarget values, it is decided, on the basis of decision criteria that arepreestablished or can be established in dependence on certainconditions, whether a departure from the route has occurred. Thisvariant has advantages especially in relatively complicated intersectionsituations (e.g., an autobahn interchange), because two testable targetparameters are available and can be taken into account in the decision.Thus, the relative turn angle can be checked initially in theinterchange area; then, at a predetermined distance after theinterchange (i.e., the path point),the direction of travel of thevehicle can be compared to the target direction of travel. This makes itpossible, for example, to unambiguously recognize turn angles of 270° ata looping turn.

The direction of travel and the change in direction can also bedetermined in continuous (sliding) fashion, and can then be comparedwith the assigned target value stored in the memory only when a givenpath point is reached. In addition, a distance rule can be established,which specifies the distance from the path point at which the averagedirection of travel should be ascertained. This is especially advisablewhen the determination of the vehicle location has a non-negligibleinaccuracy, as is the case, for example, in a GPS navigation system, dueto the consciously built-in distortion of the transmitted signals.

List of Reference Items

10 guidance system

11 on-board computer

12 input device

13 memory

14 receiver of navigational satellite system

15 display device

16 direction of travel determination device

16 a change in direction determination device

16 b comparison device

17 communications device

18 change in direction determination device

19 distance determination/comparison device

20 off-board navigation system

21 transmitter/receiver

22 traffic computer

23 digital road map

What is claimed is:
 1. A process for guiding a vehicle to a destinationpoint, comprising the steps of: determining a route to the destinationpoint in the form of consecutive path points that comprise at leastgeographic coordinates; displaying the route to a driver of the vehicle;continuously determining a current location of the vehicle based on oneof data and signals transmitted to the vehicle using a wirelesstransmission from a remote location; continuously calculating a lineardistance from the current location of the vehicle to a next one of theconsecutive path points to be passed by the vehicle; comparing thecalculated linear distance to a preestablished minimum value; replacingthe preestablished minimum value with the calculated linear distance ifthe preestablished minimum value exceeds the calculated linear distancein the step of comparing; and signalling a departure from the route ifthe calculated distance exceeds the preestablished minimum value by apredetermined threshold value.
 2. The process of claim 1, wherein saidstep of determining a route comprises using an off-board navigationsystem and transmitting the route from the off-board navigation systemto the vehicle using a wireless transmission.
 3. A vehicle guidancesystem for automatically recognizing a departure from a vehicle route,comprising: an input device for manual input of a destination point tosaid vehicle guidance system; a memory connected to said input deviceand storing said destination point; a location determination device forreceiving one of data and signals transmitted to the vehicle from anoff-board source and determining a current location of the vehicle fromsaid one of data and signals; a route determination device fordetermining the vehicle route from the current location to thedestination point and connected to said memory for storing said vehicleroute in the form of consecutive path points comprising geographiccoordinates; a display device for displaying driving instructions basedon said route and said current location; a distancedetermination/comparison device for continuously determining a lineardistance between said current location and a next one of saidconsecutive path points and for comparing said determined lineardistance to a predetermined minimum value, wherein said predeterminedminimum value is replaced by the determined linear distance if thepredetermined minimum value exceeds the determined linear distance, andwherein said distance determination/comparison device triggers a warningsignal if said determined linear distance exceeds the predeterminedminimum value by more than a predetermined threshold value.
 4. Thevehicle guidance system of claim 3, further comprising an on-boardcomputer for controlling said distance determination/comparison device.5. The vehicle guidance system of claim 4, wherein said distancedetermination/comparison device comprises a calculating program.
 6. Thevehicle guidance system of claim 3, wherein said vehicle route comprisesa plurality of sections, one of said plural sections between eachadjacent pair of said consecutive path points, and said predeterminedthreshold is set to a different specific value for each said pluralsections of said vehicle route.
 7. The vehicle guidance system of claim3, further comprising a communications device for exchanging data withan off-board navigation system.
 8. The vehicle guidance system of claim7, wherein said communications device comprises a mobile telephone. 9.The vehicle guidance system of claim 3, wherein said input devicecomprises a keyboard.
 10. The vehicle guidance system of claim 3,wherein said location determination device comprises a receiver for asatellite navigation system.
 11. The vehicle guidance system of claim 3,wherein said display device comprises a video display.
 12. The vehicleguidance system of claim 11, wherein said visual display device outputssaid travel instructions and said warning signal.